Sexual dimorphism as a facilitator of worker caste evolution in ants.

Ant societies are primarily composed of females, whereby labor is divided into reproductive, or queen, and non-reproductive, or worker, castes. Workers and reproductive queens can differ greatly in behavior, longevity, physiology, and morphology, but queen-worker differences are usually modest relative to the differences in males. Males are short-lived, typically do not provide the colony with labor, often look like a different species, and only occur seasonally. It is these differences that have historically led to their neglect in social insect research, but also why they may facilitate novel phenotypic variation - by increasing the phenotypic variability that is available for selection. In this study, worker variation in multivariate size-shape space paralleled male-queen variation. As worker variation increased within species, so did sexual variation. Across species in two independent genera, using head width as a proxy for body size, sexual size dimorphism correlated with worker polymorphism regardless of whether the ancestral condition was large or small worker/sexual dimorphism. Mounting molecular data support the hypothesis that queen-worker caste determination has co-opted many genes/pathways from sex determination. The molecular evidence, coupled with the observations from this study, leads to the hypothesis that sexual selection and selection on colony-level traits are non-independent, and that sexual dimorphism may even have facilitated the evolution of the distinct worker caste.

Growth and survival of the superorganism: Ant colony macronutrient intake and investment.

In this study, we used two common ant species (Lasius niger and Lasius neoniger) to assay how they translate variation in the diet (both in composition and frequency) into growth. We measured colony development for over 8 months and measured several phenotypic traits of the worker caste, and examined whether forager preference corresponded with diet quality. Optimal colony growth was a balance between survival and growth, and each of these was maximized with different nutrient regimes. Interestingly, forager preference was not totally aligned with the diet that maximized colony growth. Our results highlight that: (a) organism and superorganism size are controlled by the same nutrients, and this may reflect a common molecular basis for size across life's organizational levels, (b) there are nutrient trade-offs that are associated with life-history trade-offs, likely leading to selection for a balanced diet, and (c) the connection between the preference of foragers for different nutrients and how nutrient combinations affect colony success and demographics are complex and only beginning to be understood.

Functional insights from the GC-poor genomes of two aphid parasitoids, Aphidius ervi and Lysiphlebus fabarum.

BACKGROUND: Parasitoid wasps have fascinating life cycles and play an important role in trophic networks, yet little is known about their genome content and function. Parasitoids that infect aphids are an important group with the potential for biological control. Their success depends on adapting to develop inside aphids and overcoming both host aphid defenses and their protective endosymbionts. RESULTS: We present the de novo genome assemblies, detailed annotation, and comparative analysis of two closely related parasitoid wasps that target pest aphids: Aphidius ervi and Lysiphlebus fabarum (Hymenoptera: Braconidae: Aphidiinae). The genomes are small (139 and 141 Mbp) and the most AT-rich reported thus far for any arthropod (GC content: 25.8 and 23.8%). This nucleotide bias is accompanied by skewed codon usage and is stronger in genes with adult-biased expression. AT-richness may be the consequence of reduced genome size, a near absence of DNA methylation, and energy efficiency. We identify missing desaturase genes, whose absence may underlie mimicry in the cuticular hydrocarbon profile of L. fabarum. We highlight key gene groups including those underlying venom composition, chemosensory perception, and sex determination, as well as potential losses in immune pathway genes. CONCLUSIONS: These findings are of fundamental interest for insect evolution and biological control applications. They provide a strong foundation for further functional studies into coevolution between parasitoids and their hosts. Both genomes are available at https://bipaa.genouest.org.

Microbial community responses to soil tillage and crop rotation in a corn/soybean agroecosystem.

The acreage planted in corn and soybean crops is vast, and these crops contribute substantially to the world economy. The agricultural practices employed for farming these crops have major effects on ecosystem health at a worldwide scale. The microbial communities living in agricultural soils significantly contribute to nutrient uptake and cycling and can have both positive and negative impacts on the crops growing with them. In this study, we examined the impact of the crop planted and soil tillage on nutrient levels, microbial communities, and the biochemical pathways present in the soil. We found that farming practice, that is conventional tillage versus no-till, had a much greater impact on nearly everything measured compared to the crop planted. No-till fields tended to have higher nutrient levels and distinct microbial communities. Moreover, no-till fields had more DNA sequences associated with key nitrogen cycle processes, suggesting that the microbial communities were more active in cycling nitrogen. Our results indicate that tilling of agricultural soil may magnify the degree of nutrient waste and runoff by altering nutrient cycles through changes to microbial communities. Currently, a minority of acreage is maintained without tillage despite clear benefits to soil nutrient levels, and a decrease in nutrient runoff-both of which have ecosystem-level effects and both direct and indirect effects on humans and other organisms.

How Do Genomes Create Novel Phenotypes? Insights from the Loss of the Worker Caste in Ant Social Parasites.

A central goal of biology is to uncover the genetic basis for the origin of new phenotypes. A particularly effective approach is to examine the genomic architecture of species that have secondarily lost a phenotype with respect to their close relatives. In the eusocial Hymenoptera, queens and workers have divergent phenotypes that may be produced via either expression of alternative sets of caste-specific genes and pathways or differences in expression patterns of a shared set of multifunctional genes. To distinguish between these two hypotheses, we investigated how secondary loss of the worker phenotype in workerless ant social parasites impacted genome evolution across two independent origins of social parasitism in the ant genera Pogonomyrmex and Vollenhovia. We sequenced the genomes of three social parasites and their most-closely related eusocial host species and compared gene losses in social parasites with gene expression differences between host queens and workers. Virtually all annotated genes were expressed to some degree in both castes of the host, with most shifting in queen-worker bias across developmental stages. As a result, despite >1 My of divergence from the last common ancestor that had workers, the social parasites showed strikingly little evidence of gene loss, damaging mutations, or shifts in selection regime resulting from loss of the worker caste. This suggests that regulatory changes within a multifunctional genome, rather than sequence differences, have played a predominant role in the evolution of social parasitism, and perhaps also in the many gains and losses of phenotypes in the social insects.

Social supergenes of superorganisms: do supergenes play important roles in social evolution?

We suggest that supergenes, groups of co-inherited loci, may be involved in a range of intriguing genetic and evolutionary phenomena in insect societies, and may play broad roles in the evolution of cooperation and conflict. Supergenes are central in the evolution of an array of traits including self-incompatibility, mimicry, and sex chromosomes. Recently, researchers identified a large supergene, described as a social chromosome, which controls social organization in the fire ant. This system was previously considered to be a remarkable example of a single gene affecting a complex social trait. We describe how selection may commonly favor reduced recombination and the formation of supergenes for social traits, and once formed, supergenes may strongly influence further evolutionary dynamics within and between lineages. The evolution of supergenes, and even wholly non-recombining genomes, may be particularly common in systems in which genetically distinct lineages can form mutually reinforcing socially parasitic relationships.

Social insect genomes exhibit dramatic evolution in gene composition and regulation while preserving regulatory features linked to sociality.

Genomes of eusocial insects code for dramatic examples of phenotypic plasticity and social organization. We compared the genomes of seven ants, the honeybee, and various solitary insects to examine whether eusocial lineages share distinct features of genomic organization. Each ant lineage contains ∼4000 novel genes, but only 64 of these genes are conserved among all seven ants. Many gene families have been expanded in ants, notably those involved in chemical communication (e.g., desaturases and odorant receptors). Alignment of the ant genomes revealed reduced purifying selection compared with Drosophila without significantly reduced synteny. Correspondingly, ant genomes exhibit dramatic divergence of noncoding regulatory elements; however, extant conserved regions are enriched for novel noncoding RNAs and transcription factor-binding sites. Comparison of orthologous gene promoters between eusocial and solitary species revealed significant regulatory evolution in both cis (e.g., Creb) and trans (e.g., fork head) for nearly 2000 genes, many of which exhibit phenotypic plasticity. Our results emphasize that genomic changes can occur remarkably fast in ants, because two recently diverged leaf-cutter ant species exhibit faster accumulation of species-specific genes and greater divergence in regulatory elements compared with other ants or Drosophila. Thus, while the "socio-genomes" of ants and the honeybee are broadly characterized by a pervasive pattern of divergence in gene composition and regulation, they preserve lineage-specific regulatory features linked to eusociality. We propose that changes in gene regulation played a key role in the origins of insect eusociality, whereas changes in gene composition were more relevant for lineage-specific eusocial adaptations.

Patterns of DNA methylation in development, division of labor and hybridization in an ant with genetic caste determination.

BACKGROUND: DNA methylation is a common regulator of gene expression, including acting as a regulator of developmental events and behavioral changes in adults. Using the unique system of genetic caste determination in Pogonomyrmex barbatus, we were able to document changes in DNA methylation during development, and also across both ancient and contemporary hybridization events. METHODOLOGY/PRINCIPAL FINDINGS: Sodium bisulfite sequencing demonstrated in vivo methylation of symmetric CG dinucleotides in P. barbatus. We also found methylation of non-CpG sequences. This validated two bioinformatics methods for predicting gene methylation, the bias in observed to expected ratio of CpG dinucleotides and the density of CpG/TpG single nucleotide polymorphisms (SNP). Frequencies of genomic DNA methylation were determined for different developmental stages and castes using ms-AFLP assays. The genetic caste determination system (GCD) is probably the product of an ancestral hybridization event between P. barbatus and P. rugosus. Two lineages obligately co-occur within a GCD population, and queens are derived from intra-lineage matings whereas workers are produced from inter-lineage matings. Relative DNA methylation levels of queens and workers from GCD lineages (contemporary hybrids) were not significantly different until adulthood. Virgin queens had significantly higher relative levels of DNA methylation compared to workers. Worker DNA methylation did not vary among developmental stages within each lineage, but was significantly different between the currently hybridizing lineages. Finally, workers of the two genetic caste determination lineages had half as many methylated cytosines as workers from the putative parental species, which have environmental caste determination. CONCLUSIONS/SIGNIFICANCE: These results suggest that DNA methylation may be a conserved regulatory mechanism moderating division of labor in both bees and ants. Current and historic hybridization appear to have altered genomic methylation levels suggesting a possible link between changes in overall DNA methylation and the origin and regulation of genetic caste determination in P. barbatus.

The genomic impact of 100 million years of social evolution in seven ant species.

Ants (Hymenoptera, Formicidae) represent one of the most successful eusocial taxa in terms of both their geographic distribution and species number. The publication of seven ant genomes within the past year was a quantum leap for socio- and ant genomics. The diversity of social organization in ants makes them excellent model organisms to study the evolution of social systems. Comparing the ant genomes with those of the honeybee, a lineage that evolved eusociality independently from ants, and solitary insects suggests that there are significant differences in key aspects of genome organization between social and solitary insects, as well as among ant species. Altogether, these seven ant genomes open exciting new research avenues and opportunities for understanding the genetic basis and regulation of social species, and adaptive complex systems in general.

Nutritional asymmetries are related to division of labor in a queenless ant.

Eusocial species exhibit pronounced division of labor, most notably between reproductive and non-reproductive castes, but also within non-reproductive castes via morphological specialization and temporal polyethism. For species with distinct worker and queen castes, age-related differences in behavior among workers (e.g. within-nest tasks versus foraging) appear to result from physiological changes such as decreased lipid content. However, we know little about how labor is divided among individuals in species that lack a distinct queen caste. In this study, we investigated how fat storage varied among individuals in a species of ant (Dinoponera australis) that lacks a distinct queen caste and in which all individuals are morphologically similar and capable of reproduction (totipotent at birth). We distinguish between two hypotheses, 1) all individuals are physiologically similar, consistent with the possibility that any non-reproductive may eventually become reproductive, and 2) non-reproductive individuals vary in stored fat, similar to highly eusocial species, where depletion is associated with foraging and non-reproductives have lower lipid stores than reproducing individuals. Our data support the latter hypothesis. Location in the nest, the probability of foraging, and foraging effort, were all associated with decreased fat storage.

The genome sequence of the leaf-cutter ant Atta cephalotes reveals insights into its obligate symbiotic lifestyle.

Leaf-cutter ants are one of the most important herbivorous insects in the Neotropics, harvesting vast quantities of fresh leaf material. The ants use leaves to cultivate a fungus that serves as the colony's primary food source. This obligate ant-fungus mutualism is one of the few occurrences of farming by non-humans and likely facilitated the formation of their massive colonies. Mature leaf-cutter ant colonies contain millions of workers ranging in size from small garden tenders to large soldiers, resulting in one of the most complex polymorphic caste systems within ants. To begin uncovering the genomic underpinnings of this system, we sequenced the genome of Atta cephalotes using 454 pyrosequencing. One prediction from this ant's lifestyle is that it has undergone genetic modifications that reflect its obligate dependence on the fungus for nutrients. Analysis of this genome sequence is consistent with this hypothesis, as we find evidence for reductions in genes related to nutrient acquisition. These include extensive reductions in serine proteases (which are likely unnecessary because proteolysis is not a primary mechanism used to process nutrients obtained from the fungus), a loss of genes involved in arginine biosynthesis (suggesting that this amino acid is obtained from the fungus), and the absence of a hexamerin (which sequesters amino acids during larval development in other insects). Following recent reports of genome sequences from other insects that engage in symbioses with beneficial microbes, the A. cephalotes genome provides new insights into the symbiotic lifestyle of this ant and advances our understanding of host-microbe symbioses.

Draft genome of the globally widespread and invasive Argentine ant (Linepithema humile).

Ants are some of the most abundant and familiar animals on Earth, and they play vital roles in most terrestrial ecosystems. Although all ants are eusocial, and display a variety of complex and fascinating behaviors, few genomic resources exist for them. Here, we report the draft genome sequence of a particularly widespread and well-studied species, the invasive Argentine ant (Linepithema humile), which was accomplished using a combination of 454 (Roche) and Illumina sequencing and community-based funding rather than federal grant support. Manual annotation of >1,000 genes from a variety of different gene families and functional classes reveals unique features of the Argentine ant's biology, as well as similarities to Apis mellifera and Nasonia vitripennis. Distinctive features of the Argentine ant genome include remarkable expansions of gustatory (116 genes) and odorant receptors (367 genes), an abundance of cytochrome P450 genes (>110), lineage-specific expansions of yellow/major royal jelly proteins and desaturases, and complete CpG DNA methylation and RNAi toolkits. The Argentine ant genome contains fewer immune genes than Drosophila and Tribolium, which may reflect the prominent role played by behavioral and chemical suppression of pathogens. Analysis of the ratio of observed to expected CpG nucleotides for genes in the reproductive development and apoptosis pathways suggests higher levels of methylation than in the genome overall. The resources provided by this genome sequence will offer an abundance of tools for researchers seeking to illuminate the fascinating biology of this emerging model organism.

Draft genome of the red harvester ant Pogonomyrmex barbatus.

We report the draft genome sequence of the red harvester ant, Pogonomyrmex barbatus. The genome was sequenced using 454 pyrosequencing, and the current assembly and annotation were completed in less than 1 y. Analyses of conserved gene groups (more than 1,200 manually annotated genes to date) suggest a high-quality assembly and annotation comparable to recently sequenced insect genomes using Sanger sequencing. The red harvester ant is a model for studying reproductive division of labor, phenotypic plasticity, and sociogenomics. Although the genome of P. barbatus is similar to other sequenced hymenopterans (Apis mellifera and Nasonia vitripennis) in GC content and compositional organization, and possesses a complete CpG methylation toolkit, its predicted genomic CpG content differs markedly from the other hymenopterans. Gene networks involved in generating key differences between the queen and worker castes (e.g., wings and ovaries) show signatures of increased methylation and suggest that ants and bees may have independently co-opted the same gene regulatory mechanisms for reproductive division of labor. Gene family expansions (e.g., 344 functional odorant receptors) and pseudogene accumulation in chemoreception and P450 genes compared with A. mellifera and N. vitripennis are consistent with major life-history changes during the adaptive radiation of Pogonomyrmex spp., perhaps in parallel with the development of the North American deserts.

Functional proteomics of kallikrein-related peptidases in ovarian cancer ascites fluid.

Kallikrein-related peptidases (KLKs) are secreted serine proteinases with trypsin or chymotrypsin-like activity. Several family members, such as KLKs 6 and 10, are potential ovarian cancer biomarkers. Recently, using a newly developed assay for active KLK6, we found that only a very small proportion of immunoreactive KLK6 in tumor-derived clinical samples (malignant ascites fluid), in cerebrospinal fluid, and in cancer cell line supernatants is enzymatically active. We therefore hypothesized that a proportion of other immunoreactive KLKs in such samples could be present, but might be partly complexed to endogenous serine proteinase inhibitors. Using a combination of immunological isolation of the enzymes, activity-based probe analysis and proteomics, we identified active KLK10 in ovarian cancer ascites and we provide preliminary data that the activity of other KLKs present in these samples can be decreased by known proteinase inhibitors (e.g., alpha2-macroglobulin, alpha1-antitrypsin). Our data suggest that the enzymatic activity of ovarian cancer-released KLKs that are detected by regular immunoassays is low in vivo and very likely regulated by proteinase inhibitors.

Identification of five candidate lung cancer biomarkers by proteomics analysis of conditioned media of four lung cancer cell lines.

Detection of lung cancer at an early stage is necessary for successful therapy and improved survival rates. We performed a bottom-up proteomics analysis using a two-dimensional LC-MS/MS strategy on the conditioned media of four lung cancer cell lines of different histological backgrounds (non-small cell lung cancer: H23 (adenocarcinoma), H520 (squamous cell carcinoma), and H460 (large cell carcinoma); small cell lung cancer: H1688) to identify secreted or membrane-bound proteins that could be useful as novel lung cancer biomarkers. Proteomics analysis of the four conditioned media allowed identification of 1,830 different proteins (965, 871, 726, and 847 from H1688, H23, H460, and H520, respectively). All proteins were assigned a subcellular localization, and 38% were classified as extracellular or membrane-bound. We successfully identified the internal control proteins (also detected by ELISA), kallikrein-related peptidases 14 and 11, and IGFBP2. We also identified known or putative lung cancer tumor markers such as squamous cell carcinoma antigen, carcinoembryonic antigen, chromogranin A, creatine kinase BB, progastrin-releasing peptide, neural cell adhesion molecule, and tumor M2-PK. To select the most promising candidates for validation, we performed tissue specificity assays, functional classifications, literature searches for association to cancer, and a comparison of our proteome with the proteome of lung-related diseases and serum. Five novel lung cancer candidates, ADAM-17, osteoprotegerin, pentraxin 3, follistatin, and tumor necrosis factor receptor superfamily member 1A were preliminarily validated in the serum of patients with lung cancer and healthy controls. Our results demonstrate the utility of this cell culture proteomics approach to identify secreted and shed proteins that are potentially useful as serological markers for lung cancer.

Comprehensive analysis of conditioned media from ovarian cancer cell lines identifies novel candidate markers of epithelial ovarian cancer.

Ovarian cancer remains a deadly threat to women as the disease is often diagnosed in the late stages when the chance of survival is low. There are no good biomarkers available for early detection and only a few markers have shown clinical utility for prognosis, response to therapy and disease recurrence. We mined conditioned media of four ovarian cancer cell lines (HTB75, TOV-112D, TOV-21G and RMUG-S) by two-dimensional liquid chromatography-mass spectrometry. Each cell line represented one of the major histological types of epithelial ovarian cancer. We identified 2039 proteins from which 228 were extracellular and 192 were plasma membrane proteins. Within the latter list, we identified several known markers of ovarian cancer including three that are well established, namely, CA-125, HE4, and KLK6. The list of 420 extracellular and membrane proteins was cross-referenced with the proteome of ascites fluid to generate a shorter list of 51 potential biomarker candidates. According to Ingenuity Pathway Analysis, two of the top 10 diseases associated with the list of 51 proteins were cancer and reproductive diseases. We selected nine proteins for preliminary validation using 20 serum samples from healthy women and 10 from women with ovarian cancer. Of the nine proteins, clusterin (increase) and IGFBP6 (decrease) showed significant differences between women with or without ovarian cancer. We conclude that in-depth proteomic analysis of cell culture supernatants of ovarian cancer cell lines can identify potential ovarian cancer biomarkers that are worth further clinical validation.

Modeling the maintenance of a dependent lineage system: the influence of positive frequency-dependent selection on sex ratio.

In insect societies, worker versus queen development (reproductive caste) is typically governed by environmental factors, but some Pogonomyrmex seed-harvester ants exhibit strict genetic caste determination, resulting in an obligate mutualism between two reproductively isolated lineages. Queens mate randomly with multiple males from each lineage and intralineage crosses produce new queens, whereas interlineage crosses produce workers. Early colony survival is negatively frequency dependent; when lineage frequencies are unequal, queens from the rarer lineage benefit because they acquire more interlineage sperm, and produce more workers. Here we examine theoretically and empirically the effect of relative lineage frequency on sex ratio. We predict that the ratio of inter- to intralineage sperm acquired by queens of each lineage will affect the sex ratio produced at colony maturity. Consistent with model predictions, we found that gyne production in mature colonies was positively frequency dependent, increasing significantly with increasing lineage frequency across 15 populations. Unequal lineage frequencies are common and likely maintained by a complex interplay between an ecological advantage specific to one lineage, and opposing frequency-dependent selection pressures experienced throughout the colonies life-cycle; rare lineage colonies benefit during early colony growth, and common lineage colonies benefit at reproductive maturity.

Mining the ovarian cancer ascites proteome for potential ovarian cancer biomarkers.

Current ovarian cancer biomarkers are inadequate because of their relatively low diagnostic sensitivity and specificity. There is a need to discover and validate novel ovarian cancer biomarkers that are suitable for early diagnosis, monitoring, and prediction of therapeutic response. We performed an in-depth proteomics analysis of ovarian cancer ascites fluid. Size exclusion chromatography and ultrafiltration were used to remove high abundance proteins with molecular mass >/=30 kDa. After trypsin digestion, the subproteome (

Ants (Formicidae): models for social complexity.

The family Formicidae (ants) is composed of more than 12,000 described species that vary greatly in size, morphology, behavior, life history, ecology, and social organization. Ants occur in most terrestrial habitats and are the dominant animals in many of them. They have been used as models to address fundamental questions in ecology, evolution, behavior, and development. The literature on ants is extensive, and the natural history of many species is known in detail. Phylogenetic relationships for the family, as well as within many subfamilies, are known, enabling comparative studies. Their ease of sampling and ecological variation makes them attractive for studying populations and questions relating to communities. Their sociality and variation in social organization have contributed greatly to an understanding of complex systems, division of labor, and chemical communication. Ants occur in colonies composed of tens to millions of individuals that vary greatly in morphology, physiology, and behavior; this variation has been used to address proximate and ultimate mechanisms generating phenotypic plasticity. Relatedness asymmetries within colonies have been fundamental to the formulation and empirical testing of kin and group selection theories. Genomic resources have been developed for some species, and a whole-genome sequence for several species is likely to follow in the near future; comparative genomics in ants should provide new insights into the evolution of complexity and sociogenomics. Future studies using ants should help establish a more comprehensive understanding of social life, from molecules to colonies.

Collecting live ant specimens (colony sampling).

Because of the great diversity of ants, it is difficult to give a single protocol for the collection of live specimens. Ant body size can be very small or extremely large; the ants can be hard or soft, sting or spray toxic chemicals, live in the open or in hard-to-reach places; and colony size can range from tens of individuals to millions. Thus, collection techniques must be tailored to each particular species. In particular, caution must always be taken when dealing with stinging species, and symptoms and basic first-aid measures, especially for the treatment of anaphylactic shock, should be reviewed before beginning fieldwork. Nonetheless, many species are collectable as whole colonies. This protocol reviews some basic techniques for collecting ground-nesting species and describes how to collect whole live colonies (with queens), which are necessary for long-term laboratory studies and addressing questions of social organization and ecology.